1. Field of Disclosure
The disclosure relates to a cable communications system and more specifically to configuration and arrangement of an upstream in the cable communications system.
2. Related Art
Cable television (CATV) is a system of providing television, internet data, and/or other services to consumers via radio frequency signals transmitted to one or more customer premises through, but not limited to, optical fibers or coaxial cables as opposed to the over-the-air method used in traditional television broadcasting via radio waves.
A cable system may utilize Data Over Cable Service Interface Specification (DOCSIS) compliant equipment and protocols to carry out a transfer of information, such as video, audio, and/or data between one or more Set-top Devices or one or more Cable Modems (CM) and one or more cable modem termination systems (CMTS). The DOCSIS Specification generally refers to a group of specifications published by CableLabs® that define industry standards for the CMTS and the Set-top Device or the CM. In part, the DOCSIS specification sets forth requirements and objectives for various aspects of cable modem systems including operations support systems, management, data interfaces, as well as network layer, data link layer, and physical layer transport for data over cable systems. The DOCSIS interface specification entitled “Data-Over-Cable Service Interface Specifications, DOCSIS 3.0, MAC and Upper Layer Protcols Interface Specification, CM-SP-MULPIv3.0416-110623” is incorporated by reference herein in its entirety.
A DOCSIS cable system includes two primary components: one or more Set-top Devices and/or one or more CMs at a customer premises, and a CMTS located at a headend. As used herein, the term “downstream” refers to the transfer of information in a direction from the CMTS to the Set-top Devices or the CMs. The term “upstream” refers to the transfer of information in a direction from the Set-top Devices or the CMs to the CMTS. The DOCSIS specification allows for scheduling of information in DOCSIS service flows over multiple communication channels in the upstream.
DOCSIS originally provided for transmission over a single carrier, or a single communication channel at a time. In the upstream, each communication channel from among the multiple communication channels is viewed by a media access control (MAC) layer within the Set-top Devices or the CMs and/or the CMTS as a continuous stream of minislots, where a minislot represents the smallest unit of bandwidth allocation. Conventionally, these minislots are numbered in ascending sequential order using minislot numbers. The minislot numbers are used by the MAC layer in a upstream bandwidth allocation map message (MAP) to indicate which minislots are allocated to which CM.
More recent versions of DOCSIS allow for communication over multiple upstream communication channels at a time. This is termed channel bonding. Conventionally, one or more physical (PHY) layer parameters such as symbol or modulation rate, preamble length, minislot duration, modulation order, to provide some examples, of each upstream communication channel are configured independently of other upstream communication channels. Each upstream communication channel may have different capacity depending on noise and interference present on that upstream communication channel. Also, the minislots on each upstream communication channel are numbered in ascending sequential order independently of numbering of minislots of other upstream communication channels. The upstream communication channels may start numbering of their respective minislots from various starting points at various times, and count at varying rates depending on a slot size and a rate of the upstream communication channel, so at any given moment in time the current minislot numbers could be very different on different upstream communication channels.
Conventionally, the Set-top Devices or the CMs generally request upstream bandwidth by sending request messages to the CMTS. The CMTS may respond with various bandwidth grants allowing the use of one or more of the upstream communication channels. Typically, the CMTS may choose any combination of the upstream communication channels and make the bandwidth grants any length. At any given moment the CMTS may choose to distribute data differently across any of the upstream communication channels than it has previously or will in the future.
However, in practice, limits exist on the distribution of the data by the CMTS to allow for adequate system performance. For example, to minimize latency, the CMTS should not distribute the data over a very long bandwidth grant on one upstream communication channel and a very short bandwidth grant on another upstream communication channel. This would cause the CMTS to wait until the data is received from the long bandwidth grant and this would add latency to the data. Similarly, the CMTS should not distribute the data over a bandwidth grant that immediately begins on one upstream communication channel and a bandwidth grant that begins far in the future on another upstream communication channel.
As a result, the CMTS should maintain an awareness of the minislot numbering and duration represented by each minislot on each upstream communication channel and relationships of minislot numbering between upstream communication channels and timing relationships across upstream communication channels. The CMTS attempts to schedule bandwidth grants for various Set-top Devices or CMs to minimize latency while still providing fair service to all Set-top Devices or CMs. For large numbers of upstream communication channels, the complexity of tracking the slot numbering and timing relationships across upstream communication channels may be very high. In addition, the CMTS must send a separate MAP message for each upstream communication channel. This generates a large number of MAP messages when the number of upstream communication channels is large. For example, the CMTS must provide 32 separate MAPs to the Set-top Devices or the CMs, one for each upstream communication channel, when bonding 32 upstream channels which makes using a large number of upstream communication channels relatively complex.
Conventionally, the Set-top Devices or the CMs will receive multiple MAP messages for the multiple upstream communication channels in use. Each MAP message may contain a bandwidth grant to a Set-top Device or a CM. Conventionally, this bandwidth grant is indexed using the minislot numbering unique to that upstream communication channel. In order to minimize latency, the Set-top Device or the CM attempts to send earlier data in minislots that occur earlier in time, and later data in minislots that occur later in time. To do this, the Set-top Device or the CM must put the different received grants in time order across the upstream communication channels. This requires the Set-top Device or the CM to keep track of the relationships of slot numbering and duration across all upstream communication channels. For large numbers of upstream communication channels, this complexity may also be very high.
As a result of these shortcomings, channel bonding of upstream communication channels that were originally intended to be used in a single-carrier system adds a large amount of complexity to the conventional distribution of data. Thus, what is needed is a system and a method to efficiently distribute data over multiple upstream communication channels when bonding a large number of upstream communication channels to overcome the shortcomings stated above.
The disclosure will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.